LUBRICATION BY MOLECULAR MONOLAYERS AT NI-NI INTERFACES

An ultrahigh vacuum (UHV) tribometer has been used to study the frictional properties of sulfided Ni(100) surfaces modified by molecular films of ethanol ranging in thickness from submonolayer to multilayer. The instrument has been designed to allow preparation and characterization of the surfaces of pairs of metal single crystals under UHV conditions. Friction (shear) and adhesion (tensile/compressive) forces can then be measured between the two while in sliding contact. We observe very high and erratic friction forces between two Ni(100) surfaces with c(2 X 2) overlayers of sulfur. Adsorption of ethanol at coverages of greater than one monolayer results in a decrease in the coefficient of friction and sliding of one surface over the other with a well defined coefficient of friction.